Rotary switch with three-point contact support



Aug. '10,'A 11954 J. a. HODTUM 2,585,236

ROTARY SWITCH WITH THREE-POINT CONTACT SUPPORT Filed April 5, 1952 2Sheets-Sheet 1 Aug- 10, 1954 1. B. Hom-UM 2,686,236

ROTARY SWITCH WITH THREE-POINT CQNTCT SUPPORT Filed April 5, 1952 2Sheets-Sheet 2 Mvc/ow bpm/VX@ W a @www Patented Aug. 10, 1954 ROTARYSWITCH WITH THREE-POINT CONTACT SUPPORT Joseph B. Hodtum, Pittsburgh,Pa., assigner to Allis-Chalmers waukee, Wis.

yManufacturing Company, Mil- Application April 5, 1952, Serial N 0.280,711

(Cl. G-11) 13 Claims. 1

This invention relates to electrical switches, and in particular to animprovement in switches having rotary wiping members which bridgestationary blades.

In these switches in which the stationary blades are bridged on theirupper and lower Contact surfaces by a pair of rotating bridging members,the bridging members and the stationary blades must efect goodelectrical Contact regardless of which two adjacent stationary contactsare bridged. Poor electrical connection between the switch elements islikely to result from any misalignments or irregularities of theelements of the switch, and misalignment or irregularities may resultfrom manufacturing tolerances, from wear of parts of the switch or fromsludge or carbon which may accumulate on or near the switch elements.

These dihculties can be avoided to some eX- tent in switches which carryrelatively small currents by providing iiexible or resilient stationaryor movable conductive switch elements. However, the maximum currentcarrying capacity of such flexible or resilient conductive elements islimited, for if the current carried by the contact elements isrelatively large, the flexibility and resiliency of the material will beadversely affected by tempering eiect resulting from current heating.

Having in mind these diiiiculties, particularly with respect to switcheswhich carry relatively large currents and which may carry heavy shortcircuit currents, the rotating assembly of switches embodying thisinvention is constructed and assembled 'so that it has contact elementsVwhich substantially self-adjust to compensate for any wear ormisalignment of switch parts. The rotary movement of the bridgingmembers across the stationary blades is accomplished by operating ordriving mechanism to which the bridging members are independently andiioatingly connected. The self-adjustment of the contact elements isenhanced by providing three point support of the rotating, bridgingmembers. In addition, the switch is made so that the large magneticforces caused by relatively large currents flowing through the switchelements will add to the mechanical force applying the bridging membersto the stationary blades.

It is therefore an object of this invention to provide a multipleposition switch with an improved rotary contact assembly which isselfadiusting with respect to its driving mechanism and with respect tothe stationary blades engaged by the rotating assembly.

Another object of this invention is to provide a switch in which rigidconductive bridging members are embodied in a rotary contact assemblywith the bridging members independently rockable and self-adjusting toinsure their proper electrical connection with stationary blades and inwhich a resilient means unaiected by the current carried by the switchcoacts with the bridging members.

Still another object of this invention is to utilize, in an improvedmultiple position switch having rotary wiper members, the currentcarried by the switch elements to improve the electrical connectionbetween the conductive switch elements.

Still another object of this invention is to embody self-adjusting andself-positioning features in a rotating assembly of a multiple positionswitch which is small in size and easy to assemble.

Objects and advantages other than those above set forth will be apparentfrom the following description when read in connection with theaccompanying drawings, in which:

Fig. 1 is a plan view of a multiple position switch illustrating anembodiment of this invention;

Fig. 2 is an elevation view of part of the switch shown in Fig. 1;

Fig. 3 is an enlarged partial plan View of the rotating assembly of theswitch shown in Fig. 1;

Fig. 4 is a view in elevation of the assembly shown in Fig. 3;

Fig. 5 is a front elevation, partly in section, of the assembly shown inFig. 3;

Figs. 6, 7 and 8, respectively, are views similar to Figs. 3, 4 and 5,of a modification of the rotary contact assembly o1" a switch similar tothat shown in Fig. 1; and

Figs. 9 and 10, respectively, are a plan view and a partly sectionalfront view of another modication of the rotary contact assembly for theswitch shown in Fig. 1.

The switch shown in Figs. 1 to 5 has an insulating panel I I upon whicha plurality of stationary contacts I2 of suitable conductive metal arefastened by being substantially uniformlyY spaced on a full circle or onan arc of a circle. Each stationary contact may be a single pieceelement comprising a base portion I3, a terminal stud I4 and a blade I5.The blades have substantially flat contact surfaces and chamfered edgeswhich engage the rigid rotating bridging members 35, 36 of the switch.Each-stationary contact is fastened to the insulating panel by a boltI'I which are made identical to each other.

accepte extends through a hole in the insulating panel and screws intothe base portion I3. A suitable means is provided to prevent thestationary contact from turning about the axis of the bolt and is shownas a pin i8 which is inserted through the insulating panel into a recessof the base portion I3. The pin is held in the recess of the baseportion and in the insulating panel by being abutted by a washer I9between the head of bolt i'I and the panel. All the stationary contactsare similarly constructed and assembled so that the surfaces and themedian planes of the different blades are spaced substantially uniformlyfrom the panel II.

The conductive bridging members 35, 39 are rotated by a hollow driveshaft 23 to which they are fastened by connecting means in a manner toprovide independent self-adjustment of their respective positions toassure that they make good electrical contact with any of the stationaryblades. The bridging members 35, 36, the drive shaft 23 and theconnecting means constitutes a rotary contact assembly, in which theaxis X-X' of the drive shaft is normal to the surface of the insulatingpanel Il and to the median plane of blades I and extends through thatpanel at the center of the arc or circle on which the stationary bladesare positioned.

The connecting means between the drive shaft and the bridging membersincludes driving and driven surfaces which engage to transmit thedriving force of the shaft to the bridging members. In this embodiment,there is a laterally extending flat arm 29 fastened to the drive shaft23 by means of a split yoke clamp 24 which encircles the drive shaft.The split end 25 of the clamp has a threaded hole 26 for receiving abolt 21 which makes the arm 29 fast on the drive shaft with its medianplane substantially coinciding with the median plane of blades I5. Atapered pin 35 is driven through the yoke clamp 2li and the drive shaftto prevent the clamp from slipping along the shaft. The arm carries fourdrive pins 3l, 32, 33 and 34 which extend generally parallel to theshaft. One pair 3|, 32 of these pins extends from one face of the arm,while the other pair 33, 3d extends from the opposite face of the arm.These pins provide the driving surfaces. The bridging members are spacedapart along the axis of the drive shaft on opposite sides of the lateralarm and of the median plane of the blades. The driven surfaces definedby holes 45, d6, 47 and 58 in the bridging members are engaged by thecorresponding driving surfaces to effect turning of the bridging membersin either direction about the axis of the drive shaft. The driving pinshave a clearance t in the holes so that the bridging members are inloose engagement with the pins and are not restrained from 'movingsomewhat or tilting with respect to the arm.

Preferably, the bridging members are flat and On the adjacent surfacesof these members there are three protuberances which are formed asspherical buttons triangularly spaced to provide a three point supportfor each member.

Two of the three protuberances are contact buttons 38, 39 and areequally spaced from the axis of the drive shaft on the arc of thestationary blades to engage the stationary blades as the rotary contactassembly is moved. These two contact buttons are spaced apart on theirrespective bridging member a distance greater 4 than the space betweenadjacent stationary blades so that the two spherical contact buttonssimultaneously make point contact with the contact surfaces of adjacentblades. The third protuberance 44 is disposed intermediate the arc ofthe stationary blades and the drive shaft. It is midway between the twospaced holes which dene the driven surfaces of each member. This thirdprotuberance engages the lateral arm.

The stationary blades are disposed intermediate the two bridging memberswith respect to the axis of the drive shaft, and the opposite surfacesof the arm and the stationary blades are substantially aligned in theaxial direction of the shaft so that bridging members extend generallynormal of the axis of the shaft.

A biasing means is included in the rotary contact assembly to act on thebridging members to keep the driving and driven surfaces always inposition to be engaged and to create a mechanical force causing firm andpositive point contact of the protuberances of each bridging member withthe stationary blades and with the lateral arm.

The biasing means is preferably disposed in the rotary contact assemblyto act on the bridging members within the triangle defined by theprotuberances, and is held in its position by retaining means fastenedto a connecting link which extends through the bridging member. In theembodiment shown in Figs. l to 5 the connecting link is represented bybolts 5I, 52, which extend through holes 53, 54 in bridging member 36,collars 48, 49, holes 55 and 56 in bridging member 35, and holes 57, 58in a housing 59. A suitable locking device, such as nuts 6I, l62 isattached to the bolts 5I, 52; the locking device and the housing 59constitute the retaining means for the biasing means. This housing 59has two recesses 63, 64 which are lined with insulating material 65, 66,and there are two springs Bl, 68, respectively, disposed in the recesses63, 64. The shoulders formed by the heads of the bolts and by the nutsestablish lateral surfaces of the connecting link on opposite sides ofthe bridging members. These lateral surfaces are abutments whichcooperate with the springs to force the two bridging members toward eachother and to press the bridging members against the contact surfaces ofthe stationary blades.

The distance between the two bridging members is limited to apredetermined minimum value by stop means in the form of the collars 48,49 intermediate those members. The ends of these collars constitutelateral surfaces which may abut the adjacent surfaces of the twobridging members. Similarly, the lateral surfaces of the connecting linkcreated by the nuts and heads of the bolts combine with the springhousing to limit the distance between the bridging members to a maximumvalue. This control of the distance between the adjacent surfaces of thetwo bridging members to a predetermined range limits the amplitude ofoscillation of the springs to a predetermined reasonable range toprevent deterioration of the springs.

In the modified rotary contact assembly illustrated in Figs. 6, '7 and8, the arm 89 extends a greater distance laterally of the drive shaft'II than does the arm in the embodiment first described. And theconnecting link constituting the two bolts Bl, 82 which extends throughthe two bridging members 12, 'I3 also extends through holes 14, I5 inthe arm. Thus, in this second Vmeans in this Yinstance preferablycomprises cylindrical dowels 18, 19 which Yare loosely disposed in holes83, 84 in the lateral shoulder `89. The ends of these dowels may beabutted by the adjacent faces of Ythe two bridging members.

The third embodiment shown in Figs. 9 and 1-0 differs from the otherembodiments primarily vin having only one connecting bolt 9| and onespring 92. The connecting bolt extends through the bridging members 93,94 at the center of the triangle defined by the protuberances 95, 96 and91. The coil spring, which is disposed in a housing 98 made of suitableinsulating material, surrounds the bolt and is retained in its positionby the nut type locking device 99. Two dowels lill, H12 are included inthe rotary contact assembly. These dowels are spaced from the connectingbolts. rIhe end portions (H33, |04 of dowel IUI) of each of the dowelsare disposed in holes in the bridging members; while intermediateportions (I05 of dowel il) having enlarged diameters and extend throughholes in the arm |06. These dowels which are thus carried by the arm arespaced from the connecting bolt and prevent the bridging members fromturning about the longitudinal axis of the single connecting bolt, andthe lateral end surfaces of the intermediate portions may abut theadjacent surfaces of the bridging members, thereby constituting stopmeans between the bridging members.

In operation, as the drive shaft and lateral arm fast thereon arerotated about the axis of the drive shaft, the two bridging members aremoved by the driving surfaces carried by the lateral arm which engagedriven surfaces of the bridging members. The driving means isrepresented by at least two driving surfaces carried by the arm; the twodriving surfaces cooperate to prevent the bridging members from turningwith respect to the arm.

The bridging members are not rigidly connected to each other or to theirdriving means. Each of the bridging members is self-adjusting and willaccommodate for any misalignment between any parts of the switchingelements. The bridging members are free to move or rock as those membersare rotated by the driving shoulder. Each of the bridging members hasthree point support, and it is substantially impossible for them topoorly or improperly engage with the stationary blades. Biasing meansand abutment means are provided to keep the bridging members pressedagainst those stationary blades and keep the driving and driven surfacesproperly positioned to engage. Yet the bias means does not carry currentand therefore will not be tempered by current heating. In addition, thefatigue of the resilient bias means is minimized by keeping theoscillations of the resilientvmember within a predetermined range.

kThe, point of contact between the spherical surfaces of the contactbuttons and the iiat con- 6 tact surfaces of the stationary bladesenables high contact pressure to be created by both the mechanical forceof -the biasing means and the magnetic forces of the -parallelrelatively heavy currents through the two bridging members.

This switch preferably is embodied as a tap changer for a transformerwhich is disposed vin a casing filled with liquid insulation. In suchembodiments there may vbe carbon and sludge formations near the switchengaging surfaces. However, with this improved switch, the point contactbetween the bridging members and stationary blades results in lowcontact resistance, high contact pressure and self-cleaning action.

The floating action of the bridging members is very important as itresults in -a quick, automatic adjustment to give equal pressure on eachcorner of the triangular bridging member-sier perfect tap alignmentbecause the resilient member of the bias means acts on the bridgingmembers within the triangularly spaced points of support.

Another feature of this invention involves the stop means against whichthe adjacent surfaces of the bridging members abut when the distancebetween those members is reduced to the minimum. This abutment holds thetwo bridging members in what may be defined as a partially open positionwhen the tap change is being made so that the bridging members will moreeasily slide on to the next stationary blade.

Although but three embodiments of the present invention have beenillustrated and described, it will be apparent to one skilled in the artthat various changes and modications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent:

l. A switch comprising a panel, a plurality of stationary blades fixedto said panel and uniformly spaced on an arc and a moving contactassembly including two rigid conductive members, each said rigid memberhaving width greater than the space between adjacent said blades tobridge any two adjacent said blades, said rigid members being superposedon opposite sides of the median plane of said blades to provide parallelconductive paths between adjacent said blades, a shaft with its axis ofrotation perpendicular to the median plane of said blades disposed atthe center of the arc of said blades, said shaft having' a memberextending laterally of its axis in approximately the median plane ofsaid blades, driving means comprising the sole means connecting said tworigid members with said lateral member whereby said shaft rotates andmoves said rigid members, said connecting means comprising a pin xedlyattached to a first of said three members extending therefrom normal tothe median plane of said blades ,and projecting loosely through theother two said members with clearance whereby upon rotation of saidshaft said lateral member rotates said rigid members through coactingdriving and driven surfaces of said pin and of said other two membersand said rigid members are free to rock with respect to each other andwith respect to said lateral member, means coacting between said rigidmembers and said lateral member to prevent said rigid members fromturning with respect to said lateral member, and resilient meansindependent of said lateral member coacting with said two rigid membersto maintain said pin projecting through said other two members with saiddriving and driven surfaces in position to coact with each other.

2. A switch comprising a panel, a plurality of stationary blades fixedto said panel and uniformly spaced on an arc and a moving contactassembly including two conductive members, each said conductive memberhaving width greater than the space between adjacent said blades tobridge any two adjacent said blades, said conductive members beingsuperposed on opposite sides of the median plane of said blades toprovide parallel conductive bridges between adjacent said blades, ashaft with its axis of rotation perpendicular to the median plane ofsaid blades and disposed at the center of the arc of said blades, saidshaft having a member extending laterally of its axis, driving meanscomprising the sole means connecting said two conductive members withsaid lateral member whereby said shaft rotates and moves said conductivemembers, said connecting means comprising a pin xedly attached to a rstof said three members extending therefrom normal to the median plane ofsaid blades and projecting loosely through the other two said memberswith a clearance whereby upon rotation of said shaft said lateral memberrotates said conductive members through coacting driving and drivensurfaces of said pin and said other two members and said conductivemembers are free to rock with respect to each other and with respect tosaid lateral member, means coacting between said conductive members andsaid lateral member to prevent said conductive members from turning withrespect to said lateral member, and resilient means coacting with saidtwo conductive members to maintain said pin projecting through saidother two members with said driving and driven surfaces in position tocoact with each other.

3. A switch comprising a panel, a plurality of stationary blades fixedto said panel and uniformly spaced on an arc and a moving contactassembly including two conductive members, each said conductive memberhaving width greater than the space between adjacent said blades, saidconductive members superposed on opposite sides of the median plane ofsaid blades to bridge adjacent said blades to provide parallelconductive paths between two adjacent said blades, whereby`electromagnetic forces resulting from parallel plane of said blades atthe center of the arc of said blades, said shaft having a memberextending laterally of its axis, driving means comprising the sole meansconnecting said two conductive members with said lateral member wherebysaid shaft rotates and moves said conductive members, said connectingmeans comprising a first pin and a second pin iixedly attached to afirst of said members extending therefrom normal to the median plane ofsaid blades and projecting loosely through the other two of said memberswith clearance whereby upon rotation of said shaft said lateral memberrotates said conductive members through coacting driving and drivensurfaces of said pins and said other two members and each saidconductive member is free to rock with respect to the other saidmembers, said pins being spaced apart to constitute means coactingbetween said members to prevent said conductive members from turningwith respect to said lateral member and to cause said conductive membersto be moved with said lateral member, and resilient means coacting withsaid members to keep said other two members in cooperative engagementwith said pins.

4. A switch comprising a plurality of conductive blades uniformly spacedon an arc, a shaft having its axis of rotation perpendicular to themedian plane of said blades at the center of said arc, a laterallyextending arm fast on said shaft, a rotary contact assembly moved bysaid shaft, said assembly including rst and second conductive memberseach of which is wide enough to bridge two adjacent said blades, saidmembers being superposed on opposite sides of the median plane of saidblades to provide parallel paths of current through said conductivemembers between adjacent said blades, two pairs of driving pins carriedby said arm extending generally parallel to said shaft with the pins ofeach said pair of pins being spaced apart, one of said pair of pinsextending from a first face of said arm projecting loosely into saidfirst conductive member and the other of said pair of pins extendingfrom the opposite face of said arm Iprojecting loosely into said secondconductive member whereby upon rotation of said shaft said conductivemembers are moved by said pins abutting surfaces of said conductivemembers constituting the sole means connecting said conductive membersto said shaft, and resilient means to firmly hold said conductivemembers in position to be abutted by said driving pins and to press saidconductive members on said blades.

5. A switch comprising a plurality of conductive blades uniformly spacedon an arc, a shaft having its axis of rotation perpendicular to themedian plane of said blades at the center of said arc, a laterallyextending arm fast on said shaft, a rotary contact assembly moved bysaid shaft, said assembly including a pair of conductive members each ofwhich is wide enough to bridge two adjacent said blades, said memberssuperposed on opposite sides of the median plane of said blades,connecting means between said blades and said shaft including two pairsof driving pins carried by said arm extending generally parallel to saidshaft with said pairs of driving pins extending from opposite faces ofsaid arm, each of said members having driven surfaces spaced apart andloosely engaged by said driving pins, rotation of said shaft causingsaid driving pins to abut said driven surfaces constituting the solemeans connecting said members with said shaft, whereby said members arerotated about the axis of said shaft, each of said members having threeprotuberances engaging two adjacent said blades at two points and saidarm at one point to provide three point support for each of saidmembers, and resilient means to firmly hold said members in positionwith said driven surfaces disposed to be abutted by said pins and topress said members against said blades.

6. A switch comprising a plurality of conductive blades uniformly spacedon an arc, a shaft having its axis of rotation perpendicular to themedian plane of said blades at the center of said Varc and having an armextending laterally of tive members superposed. onioppositefsides voflthe median plane" of said blades, means between said members and saidlaterallyextending arms comprising two: pair of driving pins carried "bysaid arm extending generally `parallel to said shaft. saidl pairs ofdrivingl pins/extending from different faces of said'arm, each of saidmembershaving spaced driven surfaces and three protuberances,said'drivingpins inloose-engagement with saidzdriven surfacesbeingrabutted therewith upon rotation of said shaft constitutingthe'sole means connecting said, members and said shaftpand' providingfor each of said members to have independent rocking movementwith'respect to said pins, resilient means to firmly holdsaid' membersin position that said driven surfaces are abutted by said pinswhen said.shaft is rotated and to press two of said three'protuberances of eachsaid' member against two adjacent said blades. and the third of saidthree protuberances of each said member against said arm, and means toprevent the adjacent faces of saidmembers coming together when saidmembers are moved from engagement with anysaid' blade.

'7. A switch comprising a plurality of conductive blades uniformlyspaced on an arc, a shaft having its axis of rotation perpendicular tothe median plane of said blades at the center of the arm of said bladesand having an arm extending laterally of its axis, a moving contactassembly including two conductive members, said members superposed onopposite sides of the' median pla-ne ofsaid blades, adriving pin carriedby said arm, each of said members having a driven surface defining ahole loosely receiving said driving pin to be abutted bysaid driving pinupon rotation of said shaft constituting the sole means connecting saidlmembers to said shaft and' providing for independenty rockingmovement ofsaid members with respect to `Yeach other and with vrespect to saidshaft, each of said members of -a width greater thanthe space betweenadjacent said blades to bridge adjacent said blades and provideWparallel conductive paths betweenl any twol adjacentI said blades,'eachof said members'having'three-'point support and being independentlymovable with respect to' any of' the' threev pointsof support, two ofsaid` three points being on' said blades, and` biasing'means including'aspring acting on said members within said three points ofsupport.

8. A' Vswitch comprising a plurality of conductive blades uniformlyspacedY on an arc, a shaft with its' axisv of' rotation, perpendicularto the median plane'of said' blades at the center of said are having anarm `extending laterally` of its axis, and a rotarycontact assemblymovable by said shaft, saidr assembly including a pair of conductivemembers,'d'riving surfaces carried by said' arm independent of saidmembers,A driven surfaces carried by said members independent of 'saiddriving surf-aces, said driving and driven surfaces disposed to beAabutted against each other upon rotation of said shaft constituting thesoleVV means connecting said members and said arm, and biasing meansurging said members toward eachother to position said members that saiddriving and driven lsurfaces abut upon rotation of said shaft, saidmembers being substantially'identical and-each having threeprotuberances triangularly spaced with two of said protuberances beingspheroidal contact buttons on `said arc, the dista-nce between saidcontact buttons of each of said members being greater thanthedistance'betweenV 'adjacent of said blades, said membersbeingsuperposed on opposite sides of the median plane of said blades,said biasing means acting within said triangularly spaced protuberancesto cause two of said contact buttons of each of said members to make rstpoint contact with adjacent of said blades providing parallel currentpaths through said members between any two adjacent said blades and tocause the third of said protuberances of each of said members to make rmpoint contact with said arm between the arc of said blades and the axisof said shaft to provide three point support for each of said members atits said three protuberances.

9. A switch comprising a plurality of conductive blades uniformly spacedon an arc, a movable contact assembly including a pair of conductivemembers, a shaft with its axis of rotation perpendicular to the medianplane of said blades at the center of said arc having an arm extendinglaterally of its axis, means for connecting said members to said arm formoving said members across said blades by rotation of said members aboutthe axis of said shaft, said means including a pair of spaced drivingelements carried by said arm independent of said members, drivensurfaces carried by each of said members independent of said drivingelements, said driving elements disposed to abut said driven surfacesupon rotation of said shaft constituting by such abutment the sole meansconnecting said members to said arm whereby said shaft effects rotationof said members and whereby said members have independentrockingrelation with respect to said arm, said members beingsubstantially identical and each having three protuberances triangularlyspaced with two of said three protuberances being spheroidal contactbuttons on said arc spaced apart a distance greater than the spacingbetween adjacent of said blades to engage adjacent said blades, thethird of said protuberances being in contact with said arm, said membersbeing superposed on opposite sides of the median plane of said bladesproviding parallel current paths between adjacent of said blades,saidassembly including a link connecting said members and retainingsaidmembers superposed, and biasing means acting on said members withinthe triangle defined by said protuberances topress said protuberances ofeach of said members on said blades and on said arm and to hold saidmembers in position that said driving elements abut said driven surfacesupon rotation of said shaft.

10. A switch comprising a plurality of blades, an insulating panel, saidblades fastened to said panel and circumferentially spaced from eachother on an arc, a shaft movable with respect to said blades with itsaxis of rotation perpendicular to the median plane of said blades at thecenter of said arc, said shaft having a lateral member fast thereon, arotary Contact assembly comprising a rst conductive member, a secondconductive member, connecting means and biasing means, said connectingmeans including driving surfaces carried by said lateral memberindependent of said conductive members, a driven surface carried by saidfirst conductive member independent of said lateral member, a drivensurface carried by said second conductive member independent of saidlateral member, said conductive members being axially spaced along saidshaft and extending laterally of said shaft with said rst conductivemember superposed over said secondA conductive member, a first face ofsaid rst conductive member parallel to a first face of said lateralmember, a first face of said Second conductive member parallel to theopposite face of said lateral member, said driving surfaces disposedadjacent said driven surfaces whereby rotation of said shaft causes saiddriving surfaces to abut said driven surfaces constituting the solemeans connecting said rigid members to said lateral member to effectrotation of said conductive members about the axis of said shaft, themedian plane of said blades disposed between said conductive memberswith the opposite contact surfaces of each of said blades beingsubstantially normal to said axis, each of said conductive membershaving three protuberances triangularly positioned thereon, each of saidprotuberances being substantially spherical, two of said protuberanceson each of said conductive members being contact buttons disposed on thearc of said blades and spaced apart to bridge adjacent said blades andmaking substantially point contact with one of said surfaces of saidblades, the third of said protuberances of each of said conductivemembers being in contact with said lateral member intermediate said arcand said shaft whereby said three protuberances of each of saidconductive members provide three point support for said respectiveconductive member, biasing means including a link extending through saidconductive members parallel to the axis of said shaft keeping saidconductive members superposed, abutment means to limit the distancesbetween said conductive members to a predetermined maximum value andtokeep said driving and driven surfaces in position to be abutted witheach other upon rotation of said shaft, means to limit the distancebetween said conductive members to a predetermined minimum value, andresilient means acting on said conductive members within the triangledefined by said protuberances to force said protuberances of each saidconductive member into firm contact with said blades and said lateralmember.

11, A switch comprising a plurality of blades, an insulating panel, saidblades fastened to said panel and substantially uniformly spaced on anarc, a shaft movable with respect to said blades having its axis ofrotation perpendicular to the median plane of said blades at the centerof said arc and having a member extending laterally of its axis, arotary contact assembly comprising two rigid conductive members axiallyspaced apart along said shaft with said members disposed on oppositesides of said lateral member and on opposite sides of the median planeof said blades, connecting means including driving surfaces carried bysaid lateral member independent of said rigid members, a driven surfacecarried by a rst of said rigid members independent of said drivingsurfaces, a driven surface carried by the second of said rigid membersindependent of said driving surfaces, said driving surfaces disposed toabut said driven surfaces upon rotation of said shaft constituting thesole means connecting said rigid members to said lateral member toeffect rotation of said rigid members about said axis, each of saidrigid members having three spherical protuberances triangularly spacedthereon, two of said protuberances on eachV of said rigid members beingcontact buttons disposed on said arc and spaced apart circumferentiallyto bridge adjacent of said blades and making substantially point contactwith a contact surface of said blades, the third of said protuberancesof each of said rigid members making substantially point contact withsaid lateral member intermediate said arc of said shaft, and biasingmeans including a link, a spring, retaining means and abutment means,said link extending through said members parallel to the axis of saidshaft, said retaining means detachably connected to said link, saidabutmentmeans cooperating with said link and said rigid members to limitthe distance between said rigid members to a predetermined value, saidretaining means holding said spring against one of said rigid membersand cooperating with said abutment means to force said protuberances ofsaid rigid members into rm contact with said blades and said lateralmembers and to keep said driving and driven surfaces in position to beabutted with each other.

l2. A switch comprising a plurality of blades, an insulating panel, saidblades fastened to said panel and substantially uniformly spaced on anarc, a shaft movable with respect to said blades with said shaft havingits axis of rotation perpendicular to the median plane of said blades atthe center of said arc, said shaft having a member extending laterallyof its axis, a moving contact assembly comprising two rigid conductivemembers, said conductive members being spaced axially along said shafton opposite sides of said lateral member and on opposite sides of themedian plane of said blades, connecting means including driving surfacescarried by one of said three members independent of the other two saidmembers, and driven surfaces carried by each of the other two saidmembers independent of said driving surfaces, said driving surfacesdisposed adjacent said driven surface to abut said driven surfaces uponrotation of said shaft constituting the sole means connecting saidconductive members to said lateral member to` effect rotation of saidconductive members about the axis of said shaft, each of said conductivemembers having three protuberances triangularly positioned thereon withtwo of said three protuberances being spherical contact buttons on saidarc spaced apart with said two buttons of each of said conductivemembers contacting adjacent of said blades whereby each of saidconductive members bridges two adjacent of said blades, the thirdprotuberance of each of said conductive members contacting said lateralmember intermediate said arc and said axis, said three protuberances ofeach of said conductive members providing three point support for saidconductive members, and'biasing means acting on each of said conductivemembers within the triangle defined by said protuberances to force saidprotuberances against said blades and against said lateral member tokeep said driving and driven surfaces in position to abut each otherupon rotation of said shaft.

13. A switch comprising a plurality of blades, an insulating panel, saidblades fastened to said panel and substantially uniformly spaced on anarc, a shaft movable with respect to said blades, said shaft having itsaxis of rotation perpendicular to the median plane of said blades at thecenter of said arc and having a member extending laterally thereof, arotary contact assembly comprising two conductive members spaced apartaxially along said shaft and extending laterally of the axis of saidshaft with one of said conductive members superposed over the other ofvplane of said blades, the adjacent faces of each said conductive memberhaving three spherical protuberances tiia-ngulariy spaced thereon withtwo of said protuberances being contact buttons disposed on said arcmaking substantially point contact with a snrace of said blades, andspaced apart to bridge adjacent of said blades and the third saidprotuberance making point contact with said lateral amber intermediateare and said axis, biasing means disposed Within the triangle of saidprotuberances and including a link and a spring, said link carried byone of said members independent of the other two said membersconstituting driving surfaces extending through the other two saidmembers with clearance, the wall Surfaces of each said other two membersthrough which said link extends constituting driven surfaces independentof said driving surfaces, said driving surfaces being abutted saiddriven surfaces upon rotation of said shaft constituting the sole meansconnecting said conductive members to said lateral member, said Gited inthe le of this patent UNITED STATES PATENTS Number Name Date 2,491,596Venditti' Dec. 20, 1949 2,577,225 Barry Dec. 4, 1951 FOREIGN PATENTS NCountry Date 394,532 Great Britain June 29, 1933 562,938 Great BritainJuly 21, 1944

